The present invention relates to a hand-operated electrical power tool, particularly a power drill, having a rotary speed control device, an input device for entering data indicative of material to be worked on and additional data relevant to the operation of the tool, and a device for adjusting the rotary speed control device according to the entered data.
Hand-held electrical power drills are already known which are controlled by a microprocessor. In these known electrical power drills the kind of material to be worked on and diameter of the drill bit are preselectable. The microprocessor computes on the basis of the these data an optimum rotary speed which guarantees a flawless machining of the workpiece on the one hand, and prevents any damage of the drill bit or of the tool on the other hand. The computed rotary speed value is fed to a regulating circuit which adjusts the electric motor of the power drill according to this desired speed. The electronically controlled drilling machine of this kind however is rather expensive to manufacture inasmuch as apart from the central control unit there are necessary storage devices both for fixed data and for variable operational data to control the microprocessor according to a program. For preparing and entering the program additional expenses are involved and consequently the electronic circuits of microprocessor controlled drills are extremely costly and susceptible to interferences, particularly they are sensitive to stray electric fields from the electric motor.